Method and structure for forming a vertical field-effect transistor

ABSTRACT

A method for manufacturing a semiconductor device includes forming a first semiconductor layer on a semiconductor substrate, forming a second semiconductor layer including a first concentration of germanium on the first semiconductor layer, and forming a third semiconductor layer on the second semiconductor layer. The first and third semiconductor layers each have a concentration of germanium, which is greater than the first concentration of germanium. The first, second and third semiconductor layers are patterned into at least one fin. The method further includes covering the second semiconductor layer with a mask layer. In the method, a bottom source/drain region and a top source/drain region are simultaneously grown from the first semiconductor layer and the third semiconductor layer, respectively. The mask layer is removed from the second semiconductor layer, and a gate structure is formed on and around the second semiconductor layer.

TECHNICAL FIELD

The field generally relates to semiconductor devices and methods ofmanufacturing same and, in particular, to forming a vertical fieldeffect transistor (VFET) using processes that rely on a relationshipbetween critical temperature for oxide conversion and germaniumconcentration in a semiconductor layer.

BACKGROUND

Fin field-effect transistor (FinFET) devices include a transistorarchitecture that uses raised source-to-drain channel regions, referredto as fins. A FinFET device can be built on a semiconductor substrate,where a semiconductor material, such as silicon, is patterned intofin-like shapes and functions as the channels of the transistors. KnownFinFET devices include fins with source/drain regions on lateral sidesof the fins, so that current flows in a horizontal direction (e.g.,parallel to a substrate) between source/drain regions at opposite endsof the fins in the horizontal direction. As horizontal devices arescaled down, there is reduced space for metal gate and source/draincontacts, which leads to degraded short-channel control and increasedmiddle of the line (MOL) resistance.

Vertical field effect transistors (VFETs) are becoming viable deviceoptions for semiconductor devices, for example, complementary metaloxide semiconductor (CMOS) devices, beyond 7 nanometer (nm) node. VFETdevices include fin channels with source/drain regions at ends of thefin channels on top and bottom sides of the fins. Current runs throughthe fin channels in a vertical direction (e.g., perpendicular to asubstrate), for example, from a bottom source/drain region to a topsource/drain region. Vertical transport architecture devices aredesigned to extend the product value proposition beyond conventionalplateaus and address the limitations of horizontal device architecturesby, for example, decoupling of gate length from the contact gate pitch,providing a FinFET-equivalent density at a larger contacted poly pitch(CPP), and providing lower MOL resistance.

Conventional VFET integration processes are complicated, includingmultiple steps for bottom and top source/drain region, bottom and topspacer, high-k dielectric and metal gate formation. Accordingly, thereis a need for a VFET structure and method of forming same that canutilize simplified integration processes.

SUMMARY

According to an exemplary embodiment of the present invention, a methodfor manufacturing a semiconductor device includes forming a firstsemiconductor layer on a semiconductor substrate, forming a secondsemiconductor layer including a first concentration of germanium on thefirst semiconductor layer, and forming a third semiconductor layer onthe second semiconductor layer. The first and third semiconductor layerseach have a concentration of germanium, which is greater than the firstconcentration of germanium. The first, second and third semiconductorlayers are patterned into at least one fin. The method further includescovering the second semiconductor layer with a mask layer. In themethod, a bottom source/drain region and a top source/drain region aresimultaneously grown from the first semiconductor layer and the thirdsemiconductor layer, respectively. The mask layer is removed from thesecond semiconductor layer, and a gate structure is formed on and aroundthe second semiconductor layer.

According to an exemplary embodiment of the present invention, avertical field-effect transistor device includes at least one findisposed on a semiconductor substrate. The at least one fin includes asemiconductor channel layer comprising a first concentration ofgermanium. A bottom source/drain region is adjacent a lower portion ofthe at least one fin, and a top source/drain region is above thesemiconductor channel layer. The vertical field-effect transistor devicefurther includes a gate structure between the top and bottomsource/drain regions. The top and bottom source/drain regions each havea concentration of germanium, which is greater than the firstconcentration of germanium, and the gate structure is aligned with thetop source/drain region.

According to an exemplary embodiment of the present invention, a methodfor manufacturing a vertical field-effect transistor includes forming afirst semiconductor layer on a semiconductor substrate, forming a secondsemiconductor layer having a first concentration of germanium on thefirst semiconductor layer, and forming a third semiconductor layer onthe second semiconductor layer. The first and third semiconductor layerseach have a concentration of germanium, which is greater than the firstconcentration of germanium. The first, second and third semiconductorlayers are patterned into at least one fin. The method further includescovering the second semiconductor layer with a mask layer. In themethod, a bottom source/drain region and a top source/drain region aresimultaneously grown from the first semiconductor layer and the thirdsemiconductor layer, respectively, and the mask layer is removed fromthe second semiconductor layer. Top and bottom spacer layers aresimultaneously formed on the top and bottom source/drain regions,respectively, and a gate structure is formed on and around the secondsemiconductor layer.

These and other exemplary embodiments of the invention will be describedin or become apparent from the following detailed description ofexemplary embodiments, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention will be described belowin more detail, with reference to the accompanying drawings, of which:

FIG. 1 is a cross-sectional view illustrating growth of a plurality ofsemiconductor layers on a substrate in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

FIG. 2 is a cross-sectional view illustrating fin formation in a methodof manufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a first germanium oxidedeposition in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating conversion of part of thefirst germanium oxide into a first oxide mask layer in a method ofmanufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating removal of unreactedportions of the first germanium oxide and a second germanium oxidedeposition in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating conversion of part of thesecond germanium oxide into a second oxide mask layer in a method ofmanufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 7 is a cross-sectional view illustrating removal of unreactedportions of the second germanium oxide in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

FIG. 8 is a cross-sectional view illustrating removal of the first oxidemask layer and lateral recessing of the second oxide mask layer in amethod of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention.

FIG. 9 is a cross-sectional view illustrating fin hardmask removal andsimultaneous growth of bottom and top source/drain regions in a methodof manufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 10 is a cross-sectional view illustrating removal of the secondoxide mask layer and junction annealing in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention.

FIG. 11 is a cross-sectional view illustrating a third germanium oxidedeposition in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention.

FIG. 12 is a cross-sectional view illustrating conversion of part of thethird germanium oxide into top and bottom spacer layers and removal ofunreacted portions of the third germanium oxide in a method ofmanufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 13 is a cross-sectional view illustrating gate structure formationin a method of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention.

FIG. 14 is a cross-sectional view illustrating gate structure recessingin a method of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention.

FIG. 15 is a cross-sectional view illustrating gate encapsulation layerdeposition in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention.

FIG. 16 is a cross-sectional view illustrating inter-level dielectric(ILD) layer deposition in a method of manufacturing a semiconductordevice, according to an exemplary embodiment of the present invention.

FIG. 17 is a cross-sectional view illustrating patterning of the ILDlayer to form an opening for a top source/drain contact in a method ofmanufacturing a semiconductor device, according to an exemplaryembodiment of the present invention.

FIG. 18 is a cross-sectional view illustrating removal of portions ofthe top spacer and gate encapsulation layers and formation of a topsource/drain contact in a method of manufacturing a semiconductordevice, according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

Exemplary embodiments of the invention will now be discussed in furtherdetail with regard to semiconductor devices and methods of manufacturingsame and, in particular, to VFET devices manufactured based on arelationship between critical temperature for silicon germanium tosilicon oxide conversion and germanium concentration in a silicongermanium layer.

It is to be understood that the various layers and/or regions shown inthe accompanying drawings are not drawn to scale, and that one or morelayers and/or regions of a type commonly used in, for example, FinFET,VFET, CMOS, field-effect transistor (FET), nanowire FET, nanosheet FETs,metal-oxide-semiconductor field-effect transistor (MOSFET), singleelectron transistor (SET) and/or other semiconductor devices may not beexplicitly shown in a given drawing. This does not imply that the layersand/or regions not explicitly shown are omitted from the actual devices.In addition, certain elements may be left out of particular views forthe sake of clarity and/or simplicity when explanations are notnecessarily focused on the omitted elements. Moreover, the same orsimilar reference numbers used throughout the drawings are used todenote the same or similar features, elements, or structures, and thus,a detailed explanation of the same or similar features, elements, orstructures will not be repeated for each of the drawings.

The semiconductor devices and methods for forming same in accordancewith embodiments of the present invention can be employed inapplications, hardware, and/or electronic systems. Suitable hardware andsystems for implementing embodiments of the invention may include, butare not limited to, personal computers, communication networks,electronic commerce systems, portable communications devices (e.g., celland smart phones), solid-state media storage devices, functionalcircuitry, etc. Systems and hardware incorporating the semiconductordevices are contemplated embodiments of the invention. Given theteachings of embodiments of the invention provided herein, one ofordinary skill in the art will be able to contemplate otherimplementations and applications of embodiments of the invention.

The embodiments of the present invention can be used in connection withsemiconductor devices that may require, for example, FinFETs, VFETs,CMOSs, FETs, nanowire FETs, nanosheet FETs, SETs, and/or MOSFETs. By wayof non-limiting example, the semiconductor devices can include, but arenot necessarily limited to FinFET, VFET, CMOS, FET, nanowire FET,nanosheet FET, SET, CMOS and MOSFET devices, and/or semiconductordevices that use FinFET, VFET, CMOS, FET, nanowire FET, nanosheet FET,SET, CMOS and/or MOSFET technology.

As used herein, “height” refers to a vertical size of an element (e.g.,a layer, trench, hole, opening, etc.) in the cross-sectional viewsmeasured from a bottom surface to a top surface of the element, and/ormeasured with respect to a surface on which the element is located.Conversely, a “depth” refers to a vertical size of an element (e.g., alayer, trench, hole, opening, etc.) in the cross-sectional viewsmeasured from a top surface to a bottom surface of the element. Termssuch as “thick”, “thickness”, “thin” or derivatives thereof may be usedin place of “height” where indicated.

As used herein, “lateral,” “lateral side,” “lateral surface” refers to aside surface of an element (e.g., a layer, opening, etc.), such as aleft or right side surface in the drawings.

As used herein, “width” or “length” refers to a size of an element(e.g., a layer, trench, hole, opening, etc.) in the drawings measuredfrom a side surface to an opposite surface of the element. Terms such as“thick”, “thickness”, “thin” or derivatives thereof may be used in placeof “width” or “length” where indicated.

As used herein, terms such as “upper”, “lower”, “right”, “left”,“vertical”, “horizontal”, “top”, “bottom”, and derivatives thereof shallrelate to the disclosed structures and methods, as oriented in thedrawing figures. For example, as used herein, “vertical” refers to adirection perpendicular to the top surface of the substrate in thecross-sectional views, and “horizontal” refers to a direction parallelto the top surface of the substrate in the cross-sectional views.

As used herein, unless otherwise specified, terms such as “on”,“overlying”, “atop”, “on top”, “positioned on” or “positioned atop” meanthat a first element is present on a second element, wherein interveningelements may be present between the first element and the secondelement. As used herein, unless otherwise specified, the term “directly”used in connection with the terms “on”, “overlying”, “atop”, “on top”,“positioned on” or “positioned atop” or the term “direct contact” meanthat a first element and a second element are connected without anyintervening elements, such as, for example, intermediary conducting,insulating or semiconductor layers, present between the first elementand the second element.

Embodiments of the present invention correspond to methods offabricating and structures for VFETs, which allow for simultaneousformation of top and bottom source/drain regions and simultaneousformation of top and bottom spacers. In accordance with embodiments ofthe present invention, recessed gate structures including, for example,a high-k dielectric and a gate conductor, are self-aligned withpreviously formed top source/drain regions. In addition, top and bottomspacers formed around epitaxially grown source/drain regions reduceparasitic capacitance. Embodiments of the present invention also providea source/drain contact having a larger volume than conventionalstructures, and consequently lower resistance.

FIG. 1 is a cross-sectional view illustrating growth of a plurality ofsemiconductor layers on a substrate in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention. Referring to FIG. 1, semiconductor layers 107 a, 108and 107 b are epitaxially grown on a semiconductor substrate 102. Inaccordance with an embodiment of the present invention, the substrate102 comprises, a semiconductor material including, but not necessarilylimited to, silicon (Si), silicon carbide (SiC), Si:C (carbon dopedsilicon), a II-V or III-V compound semiconductor or other likesemiconductor. In addition, multiple layers of the semiconductormaterials can be used as the semiconductor material of the substrate102. In accordance with an embodiment of the present invention, thesemiconductor layers 107 a, 108 and 107 b each comprise a semiconductormaterial including, but not necessarily limited to, silicon germanium(SiGe) or other semiconductor material including germanium. Thesemiconductor layers 107 a and 107 b have a different concentration ofgermanium from semiconductor layer 108. For example, the semiconductorlayers 107 a and 107 b include SiGe with about 20% to about 40%germanium, and the semiconductor layer 108 includes SiGe with a lowerconcentration of germanium than the semiconductor layers 107 a and 107b, for example, about 10% to about 20% germanium. In a non-limitingexample, the semiconductor layers 107 a and 107 b, and 108 respectivelycomprise SiGe with 40% and 20% germanium, but the embodiments of thepresent invention are not necessarily limited thereto. In accordancewith an embodiment of the present invention, a resulting vertical height(e.g., thickness) of the semiconductor layer 107 a after epitaxialgrowth is about 20 nm-about 60 nm, a resulting vertical height (e.g.,thickness) of the semiconductor layer 108 after epitaxial growth isabout 15 nm-about 40 nm, and a resulting vertical height (e.g.,thickness) of the semiconductor layer 107 b after epitaxial growth isabout 5 nm-about 20 nm.

Terms such as “epitaxial growth and/or deposition” and “epitaxiallyformed and/or grown” refer to the growth of a semiconductor material ona deposition surface of a semiconductor material, in which thesemiconductor material being grown has the same crystallinecharacteristics as the semiconductor material of the deposition surface.In an epitaxial deposition process, the chemical reactants provided bythe source gases are controlled and the system parameters are set sothat the depositing atoms arrive at the deposition surface of thesemiconductor substrate with sufficient energy to move around on thesurface and orient themselves to the crystal arrangement of the atoms ofthe deposition surface. Therefore, an epitaxial semiconductor materialhas the same crystalline characteristics as the deposition surface onwhich it is formed. For example, an epitaxial semiconductor materialdeposited on a {100} crystal surface will take on a {100} orientation.In some embodiments, epitaxial growth and/or deposition processes areselective to forming on a semiconductor surface, and do not depositmaterial on dielectric surfaces, such as silicon dioxide or siliconnitride surfaces.

Examples of various epitaxial growth processes include, for example,rapid thermal chemical vapor deposition (RTCVD), low-energy plasmadeposition (LEPD), ultra-high vacuum chemical vapor deposition (UHVCVD),atmospheric pressure chemical vapor deposition (APCVD) and molecularbeam epitaxy (MBE). The temperature for an epitaxial deposition processcan range from 500° C. to 900° C. Although higher temperature typicallyresults in faster deposition, the faster deposition may result incrystal defects and film cracking.

A number of different sources may be used for the epitaxial growth ofthe compressively strained layer. In some embodiments, a gas source forthe deposition of epitaxial semiconductor material includes a siliconcontaining gas source, a germanium containing gas source, or acombination thereof. For example, an epitaxial silicon layer may bedeposited from a silicon gas source including, but not necessarilylimited to, silane, disilane, ldisilane, trisilane, tetrasilane,hexachlorodisilane, tetrachlorosilane, dichlorosilane, trichlorosilane,and combinations thereof. An epitaxial germanium layer can be depositedfrom a germanium gas source including, but not necessarily limited to,germane, digermane, halogermane, dichlorogermane, trichlorogermane,tetrachlorogermane and combinations thereof. While an epitaxial silicongermanium alloy layer can be formed utilizing a combination of such gassources. Carrier gases like hydrogen, nitrogen, helium and argon can beused.

FIG. 2 is a cross-sectional view illustrating fin formation in a methodof manufacturing a semiconductor device, according to an exemplaryembodiment of the present invention. Referring to FIG. 2, the layers 107a, 108 and 107 b on the substrate 102 are patterned into a plurality offins including of portions of the layers 107 a, 108 and 107 b, which areeach under a hardmask layer 110. A portion of the layer 107 a is notpatterned into fins and remains on the substrate 102. For ease ofexplanation, three fins are shown in FIG. 2. However, the embodiments ofthe present invention are not necessarily limited thereto, and thelayers 107 a, 108 and 107 b can be patterned into more or less thanthree fins.

According to an embodiment, the hardmasks 110 including, for example, adielectric material, such as silicon nitride (SiN) or a combination ofmultiple materials, are formed on the portions of the blanket layers 107a, 108 and 107 b that are to be formed into the fins. The fin patterningcan be done by various patterning techniques, including, but notnecessarily limited to, directional etching and/or a sidewall imagetransfer (SIT) process, for example. The SIT process includes usinglithography to form a pattern referred to as a mandrel. The mandrelmaterial can include, but is not limited to, amorphous silicon oramorphous carbon. After the mandrel formation, a conformal film can bedeposited and then followed by an etchback. The conformal film will formspacers at both sides of the mandrel. The spacer material can include,but is not limited, oxide or SiN. After that, the mandrel can be removedby reactive ion etching (RIE) processes. As a result, the spacers willhave half the pitch of the mandrel. In other words, the pattern istransferred from a lithography-defined mandrel to spacers, where thepattern density is doubled. The spacer pattern can be used as the hardmask to form the fins by RIE processes. Alternatively, fin patterningcan be done by any other suitable patterning technique, including butnot limited to, lithography (e.g., extreme ultraviolet (EUV)) inconjunction with ME, self-aligned double patterning (SADP), self-alignedmultiple patterning (SAMP), and/or self-aligned quadruple patterning(SAQP)).

FIG. 3 is a cross-sectional view illustrating a first germanium oxidedeposition in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention. Referringto FIG. 3, a first germanium oxide (GeO₂) layer 120 is deposited using,for example, atomic layer deposition (ALD) or other conformal depositionprocess, on the structure from FIG. 2, including on the stackedstructures including the remaining portions of layers 107 a, 108 and 107b, on the hardmask layer 110, and on the exposed portions of theunpatterned portions of the layer 107 a on the substrate 102. In anon-limiting embodiment, a thickness of the GeO₂ layer 120 can be in therange of about 2 nm-about 6 nm.

FIG. 4 is a cross-sectional view illustrating conversion of part of thefirst germanium oxide into a first oxide mask layer in a method ofmanufacturing a semiconductor device, according to an exemplaryembodiment of the present invention. Referring to FIG. 4, afterdeposition of the GeO₂ layer 120, a thermal annealing process isperformed in, for example, nitrogen (N₂), argon (Ar), helium (He), xenon(Xe), and/or hydrogen (H₂). The temperature at which the thermalannealing process is performed and the germanium concentration of eachof the semiconductor layers 107 a, 108 and 107 b control whether a masklayer is formed on the semiconductor layers 107 a, 108 and 107 b. Inaccordance with an embodiment of the present invention, the requiredannealing temperature to convert a GeO₂ layer (e.g., GeO₂ layer 120) onSiGe layers 107 a, 108 and 107 b to, for example, a silicon oxide layer(e.g., layer 130) is inversely proportional to the germaniumconcentration in the SiGe semiconductor layers 107 a, 108 and 107 b. Inother words, as the concentration of germanium in SiGe decreases, thetemperature required to convert the GeO₂ layer to the mask layerincreases. According to a non-limiting embodiment, for respectivegermanium concentration ranges of about 10% to about 20%, and about 20%to about 40%, the corresponding annealing temperature ranges to permitconversion to silicon oxide are about 650° C. to about 750° C., andabout 550° C. to about 650° C., respectively.

Referring back to FIG. 4, the annealing process is controlled so thatthe first oxide mask layer 130 is selectively formed on the lowersemiconductor and upper semiconductor layers 107 a and 107 b, but not onthe semiconductor layer 108. Assume for purposes of illustration thatthe lower and upper semiconductor layers 107 a and 107 b comprise SiGewith 40% germanium. In order to selectively form the mask layer 130 onsemiconductor layers 107 a and 107 b, the thermal annealing is performedat a temperature of, for example, about 550° C., so that the mask layer130 is not formed on the semiconductor layers 108 having SiGe with lowerconcentrations of germanium. Alternatively, a much thinner mask layer130 is formed, which can be completely removed from semiconductor layers108 by etching, while leaving a substantial amount of mask layer onlayers 107 a and 107 b.

As a result, the thermal annealing process results in the conversion ofthe GeO₂ layer 120 into the layers 130 on the layers 107 a and 107 b,which, in this example, comprise SiGe with a germanium concentration of40%. The layers 130 comprise silicon oxide (SiO_(x)), where x is, forexample, 2 in the case of silicon dioxide (SiO₂), or 1.99 or 2.01. Forease of explanation, the disclosure will refer to the layers 130 as SiO₂layers. It is to be understood that the germanium concentrations of thelayers 107 a, 108 and 107 b may vary, and the annealing processconditions (e.g., temperature) may be adjusted to ensure selectiveformation of the SiO₂ layers on the desired semiconductor layers 107 a,108 or 107 b.

As can be seen in FIG. 4, the thermal annealing process does not causethe GeO₂ layer 120 on the SiGe layers 108, and on the hardmask layer 110(e.g., SiN) to be converted into SiO₂.

FIG. 5 is a cross-sectional view illustrating removal of unreactedportions of the first germanium oxide and a second germanium oxidedeposition in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention. Referringto FIG. 5, the unreacted portions of the first GeO₂ layer 120 are watersoluble, and are removed using, for example, a water based agent, suchas, for example, deionized (DI) water. The unreacted portions of theGeO₂ layer 120 are removed from the stacked structures including thehardmask layers 110, and the layers 108.

After removal of the unreacted portions of the GeO₂ layer 120, secondgermanium oxide (GeO₂) layer 220 is deposited using, for example, ALD orother conformal deposition process, on the stacked structures includingthe layers 107 a, 108 and 107 b and the hardmask layer 110, on the SiO₂layers 130 and on the exposed portions of the unpatterned portions ofthe layer 107 a on the substrate 102. In a non-limiting embodiment, athickness of the second GeO₂ layer 220 can be in the range of about 5nm-about 15 nm, which is thicker than the first GeO₂ layer 120. As canbe seen portions of the second GeO₂ layer 220 formed on the SiO₂ layers130 extend further outward than portions formed, for example, directlyon the fins and/or hardmasks 110.

FIG. 6 is a cross-sectional view illustrating conversion of part of thesecond germanium oxide into a second oxide mask layer in a method ofmanufacturing a semiconductor device, according to an exemplaryembodiment of the present invention. Referring to FIG. 6, afterdeposition of the second GeO₂ layer 220, a thermal annealing process isperformed in, for example, N₂, Ar, He, Xe, and/or H₂. As noted above,the temperature at which the thermal annealing process is performed andthe germanium concentration of each of the semiconductor layers 107 a,108 and 107 b control whether a mask layer is formed on thesemiconductor layers 107 a, 108 and 107 b. With respect to FIG. 6, as aresult of the annealing process, a second oxide mask layer 230 isselectively formed on the semiconductor layer 108, but not on thesemiconductor layers 107 a and 107 b. The presence of the first oxidemask layers 130 on layers 107 a and 107 b prevents an additional oxidelayer from being formed on the first oxide mask layers 130 because theunderlying SiGe layers 107 a and 107 b are masked by the first oxidemask layers 130. In other words, even though the temperature to causeconversion to silicon oxide of the second GeO₂ layer 220 on the lowergermanium concentration SiGe layers 108 must be higher than that tocause conversion of GeO₂ to silicon oxide on higher concentration SiGelayers 107 a and 107 b, the presence of the first oxide mask layers 130on layers 107 a and 107 b prevents an additional SiO₂ layer from beingformed.

Assume for purposes of illustration that the semiconductor layer 108comprises SiGe with 20% germanium. In order to form the mask layer 230on semiconductor layer 108, the thermal annealing is performed at atemperature of, for example, about 650° C. Since the lower and uppersemiconductor layers 107 a and 107 b having SiGe with a higherconcentration of germanium than that of the layers 108 are masked withthe SiO₂ layers 130 from the previous annealing process, the portion ofthe second GeO₂ layer 220 formed on the SiO₂ layers 130 will not reactduring this next annealing process. As a result, the thermal annealingprocess in connection with FIG. 6 results in the conversion of thesecond GeO₂ layer 220 into the layers 230 on the layers 108, which, inthis example, comprise SiGe with a germanium concentration of 20%. Likethe layers 130, the layers 230 comprise silicon oxide (SiO_(x)), where xis, for example, 2 in the case of silicon dioxide (SiO₂), or 1.99 or2.01. For ease of explanation, the disclosure will refer to the layers230 as SiO₂ layers. The resulting SiO₂ layers 230 are thicker (e.g.,horizontal thickness) than the SiO₂ layers 130.

As can be seen in FIG. 6, the thermal annealing process does not causethe second GeO₂ layer 220 on the SiGe layers 107 a and 107 b (includingon SiO₂ layers 130), and on the hardmask layers 110 to be converted intoSiO₂.

FIG. 7 is a cross-sectional view illustrating removal of unreactedportions of the second germanium oxide in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention. Referring to FIG. 7, the unreacted portions of thesecond GeO₂ layer 220 are water soluble, and are removed using, forexample, a water based agent, such as, for example, DI water. Theunreacted portions of the GeO₂ layer 220 are removed from the stackedstructures including the hardmask layers 110, and the layers 107 a and107 b. The unreacted portions of the GeO₂ layer 220 are also removedfrom the unpatterned portions of the layer 107 a on the semiconductorsubstrate 102.

According to an embodiment of the present invention, during the thermalannealing processes, the annealing conditions cause the Si in the SiGeportions 107 a, 108 and 107 b to bond with the oxygen in the GeO₂ layers120 or 220 to form SiO₂ layers 130 or 230. The Si in the SiGe portions107 a, 108 and 107 b does not bond with the Ge in the respective GeO₂layers 120 and 220. As a result, the Ge from the GeO₂ layers 120 and 220is driven into the inner portions of the layers 107 a and 107 b, and108, respectively, and the Si from the inner portions of the layers 107a, 107 b and 108 is driven out of the layers 107 a, 107 b and 108 tobond with the oxygen, which forms higher Ge % SiGe portions 107 a, 107 band 108. The resulting Ge concentration in the SiGe portions 107 a, 107b and 108 after thermal annealing is higher than the Ge concentration inthose layers prior to the thermal annealing.

In accordance with embodiments of the present invention, the annealingcan be performed in an environment including nitrogen, argon, xenon,helium, hydrogen, or any suitable combination of those gases, for a timeperiod of 1 millisecond to 30 minutes. The anneal can be done by rapidthermal annealing (RTP), furnace annealing, flash annealing, laserannealing, spike annealing, or any suitable combination of thosetechniques.

In accordance with an embodiment of the present invention, the annealingmay be carried out for a variable period of time. In one example, theannealing process is carried out for a time period from about 0.5seconds to 2 seconds, depending on temperature and germaniumconcentration in the SiGe layers 107 a, 108 and 107 b. The annealingprocess may be carried out at a single targeted temperature, or atvarious ramp and soak cycles using various ramp rates and soak times.

By way of further explanation, in accordance with an embodiment of thepresent invention, the Si atoms in the SiGe portions 107 a, 108 and 107b bond with available oxygen from the respective GeO₂ layers 120 and 220during the annealing processes to form the SiO₂ layers 130 and 230.

FIG. 8 is a cross-sectional view illustrating removal of the first oxidemask layer and lateral recessing of the second oxide mask layer in amethod of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention. Referring to FIG. 8, thethinner SiO₂ layers 130 are removed to expose the layers 107 a and 107 bhaving, for example, SiGe with 40% germanium concentration. The removalof the Sift layers 130 is performed using a wet or dry etch processincluding, for example, diluted hydrofluoric (HF) acid solution. Theetch process reduces a thickness of the remaining SiO₂ layers 230, whichwere thicker than the SiO₂ layers 130. For example, the etch processreduces a thickness of the remaining SiO₂ layers 230 by about half if athickness of the SiO₂ layers 230 was about twice the thickness of theSiO₂ layers 130.

FIG. 9 is a cross-sectional view illustrating fin hardmask removal andsimultaneous growth of bottom and top source/drain regions in a methodof manufacturing a semiconductor device, according to an exemplaryembodiment of the present invention. Referring to FIG. 9, the hardmasks110 are selectively removed with respect to the SiGe layers 107 a and107 b, and the SiO₂ layers 230, using for example, a selective etchprocess. The selective etch process can include, for example, a wet etchprocess containing phosphoric acid.

Following the fin hardmask removal, with the semiconductor layers 108protected by the remaining SiO₂ layers 230, bottom and top source/drainregions 141 and 142 are simultaneously epitaxially grown in an epitaxialgrowth process from the semiconductor layers (e.g., SiGe) 107 a and 107b. The epitaxially grown bottom and top source/drain regions 141 and 142can be in-situ doped, meaning dopants are incorporated into the epitaxyfilm during the epitaxy process. Other alternative doping techniques canbe used, including but not limited to, for example, ion implantation,gas phase doping, plasma doping, plasma immersion ion implantation,cluster doping, infusion doping, liquid phase doping, solid phasedoping, etc., and dopants may include, for example, an n-type dopantselected from a group of phosphorus (P), arsenic (As) and antimony (Sb),and a p-type dopant selected from a group of boron (B), gallium (Ga),indium (In), and thallium (Tl) at various concentrations. For example,in a non-limiting example, a dopant concentration range may be1×10¹⁸/cm³ to 3×10²¹/cm³. Since the semiconductor layers 108 are coveredby the remaining SiO₂ layers 230 during epitaxial growth, the bottom andtop source/drain regions 141 and 142 can be epitaxially grown at thesame time. In accordance with an embodiment of the present invention,the bottom and top source/drain regions 141 and 142 can also be doped atthe same time. The bottom and top source/drain regions 141 and 142 havethe same or similar germanium concentration as the semiconductor layers107 a and 107 b from which they are grown, with the addition of adopant. Example Ge % in source/drain regions 141 and 142 is about40%-about 85%.

FIG. 10 is a cross-sectional view illustrating removal of the secondoxide mask layer and junction annealing in a method of manufacturing asemiconductor device, according to an exemplary embodiment of thepresent invention. Referring to FIG. 10, the SiO₂ layers 230 are removedfrom the layers 108. The removal of the Sift layers 230 is performedusing a wet or dry etch process including, for example, diluted HFsolution.

As can be seen from FIG. 10, junction annealing is performed. The bottomjunctions 141′ between the bottom source/drain regions 141 and the fins,and the top junctions 142′ between the top source/drain regions 142 andthe fins, are formed by an annealing process. The annealing processcauses dopant diffusion into the layers 107 a and parts of the layers108 from the bottom source/drain regions 141, and dopant diffusion intothe layers 107 b and parts of the layers 108 from the top source/drainregions 142. The resulting bottom and top junctions 141′ and 142′include the portions formerly labeled as 107 a and 107 b, and parts oflayer 108, which retain the same shape and include SiGe, but afterdiffusion also include the diffused dopant. A doping concentration canbe higher at areas of the fins closer to the top and bottom source/drainregions 141 and 142 than at areas of the fins farther away from thesource/drain regions 141 and 142. The annealing process can be, forexample, a drive-in annealing process performed at temperatures in therange of, for example, about 800° C. to 1300° C. and for durations inthe range of, for example, about 0.01 seconds to 10 minutes. The annealcan be done by rapid thermal annealing (RTP), furnace annealing, flashannealing, laser annealing, spike annealing, or any suitable combinationof those techniques.

FIG. 11 is a cross-sectional view illustrating a third germanium oxidedeposition in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention. Referringto FIG. 11, a third GeO₂ layer 320 is deposited using, for example,atomic layer deposition (ALD) or other conformal deposition process, onthe structure from FIG. 10, including on the stacked structuresincluding the remaining portions of layers 108, the top and bottomsource/drain regions 142 and 141, and the top and bottom junctions 142′and 141′. In a non-limiting embodiment, a thickness of the third GeO₂layer 320 can be in the range of about 3 nm-about 8 nm.

FIG. 12 is a cross-sectional view illustrating conversion of part of thethird germanium oxide into top and bottom spacer layers and removal ofunreacted portions of the third germanium oxide in a method ofmanufacturing a semiconductor device, according to an exemplaryembodiment of the present invention. Referring to FIG. 12, a thermalannealing process to convert the third GeO₂ layer 320 to silicon oxideis controlled so that top and bottom spacer layers 332 and 331 aresimultaneously selectively formed on the top and bottom source/drainregions 142 and 141, which have the same or similar germaniumconcentration to layers 107 a and 107 b prior to the junction annealing.With the exception of areas that are closely adjacent to the top andbottom source/drain regions 142 and 141, the top and bottom spacerlayers 332 and 331 are not formed on the semiconductor layers 108 orjunction annealed portions of the semiconductor layers 108. Assume forpurposes of illustration that the top and bottom source/drain regions142 and 141 comprise SiGe with 50% germanium. In order to selectivelyform the top and bottom spacer layers 332 and 331 on the top and bottomsource/drain regions 142 and 141, the thermal annealing is performed ata temperature of, for example, about 500° C., so that the top and bottomspacer layers 332 and 331 are not formed on the semiconductor layers 108or junction annealed portions of the semiconductor layers 108 havingSiGe with lower concentrations of germanium. As a result, the thermalannealing process results in the conversion of the GeO₂ layer 320 intothe layers 332 and 331 on the top and bottom source/drain regions 142and 141 b, which, in this example, comprise SiGe with a germaniumconcentration of 50%. The layers 331 and 332 comprise silicon oxide(SiOx), where x is, for example, 2 in the case of silicon dioxide(SiO₂), or 1.99 or 2.01. For ease of explanation, the disclosure willrefer to the layers 331 and 332 as SiO₂ layers. It is to be understoodthat the germanium concentrations of the top and bottom source/drainregions 142 and 141, and of the semiconductor layers 108 or junctionannealed portions of the semiconductor layers 108, may vary, and theannealing process conditions (e.g., temperature) may be adjusted toensure selective formation of the SiO₂ top and bottom spacer layers 332and 331 on the desired top and bottom source/drain regions 142 and 141.The annealing process and conditions to convert the third GeO₂ layers320 to the top and bottom spacers 332 and 331 are the same or similar tothe annealing process and conditions described above in connection withconverting first or second GeO₂ layers 120 or 220 to the SiO₂ layers 130or 230.

The unreacted GeO₂ layers 320 on the semiconductor layers 108 orjunction annealed portions of the semiconductor layers 108 are watersoluble, and are removed using, for example, a water based agent, suchas, for example, DI water. The unreacted portions of the GeO₂ layer 320are removed from the stacked structures including the semiconductorlayers 108 or junction annealed portions of the semiconductor layers108.

FIG. 13 is a cross-sectional view illustrating gate structure formationin a method of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention. Referring to FIG. 13, thegate structures include gate layers 155 and dielectric layers 150. Thedielectric layers 150 include, for example, a high-K material includingbut not necessarily limited to, HfO₂ (hafnium oxide), ZrO₂ (zirconiumdioxide), hafnium zirconium oxide Al₂O₃ (aluminum oxide), and Ta₂O₅(tantalum pentoxide). The gate layers 155 include, for example, awork-function metal (WFM) layer, including but not necessarily limitedto, for a p-type FET (pFET), titanium nitride (TiN), tantalum nitride(TaN) or ruthenium (Ru), and for an n-type FET (nFET), TiN, titaniumaluminum nitride (TiAlN), titanium aluminum carbon nitride (TiAlCN),titanium aluminum carbide (TiAlC), tantalum aluminum carbide (TaAlC),tantalum aluminum carbon nitride (TaAlCN) or lanthanum (La) doped TiN,TaN. The gate layers 155 further include a gate conductor including, butnot limited to amorphous silicon (a-Si), or metals, such as, forexample, tungsten, cobalt, zirconium, tantalum, titanium, aluminum,ruthenium, copper, metal carbides, metal nitrides, transition metalaluminides, tantalum carbide, titanium carbide, tantalum magnesiumcarbide, or combinations thereof.

The gate structures are deposited on the spacers 331 and 332 on thesource/drain regions 141 and 142 and on and around the fins includingthe semiconductor layers 108 and junction annealed portions of thesemiconductor layers 108. The gate structures are deposited using, forexample, deposition techniques including, but not limited to, chemicalvapor deposition (CVD), plasma enhanced CVD (PECVD), radio-frequency CVD(RFCVD), physical vapor deposition (PVD), atomic layer deposition (ALD),molecular layer deposition (MLD), molecular beam deposition (MBD),pulsed laser deposition (PLD), liquid source misted chemical deposition(LSMCD), sputtering, and/or plating, followed by a planarizationprocess, such as, for example, chemical mechanical planarization (CMP).

FIG. 14 is a cross-sectional view illustrating gate structure recessingin a method of manufacturing a semiconductor device, according to anexemplary embodiment of the present invention. Referring to FIG. 14, thegate structures including the gate layers 155 and the dielectric layers150 are recessed and removed. In some embodiments, the gate recessprocess comprises a first etch process (e.g., RIE) that etches gatelayers 155 selective to the high-K gate dielectric 150, and a secondgate dielectric etch process (e.g., isotropic high-K dielectric etch) toremove the exposed high-K gate dielectric. As can be seen, using thegate structures are selectively etched with respect to the top andbottom spacers 332 and 331, so that the gate structures under the topspacers 332 and the top source/drain regions 142 remain, while theexposed portions of the gate structures are removed. As a result, theremaining portions of the gate structures are self-aligned with the topspacers 332 and the top source/drain regions 142. The gate structuresincluding the gate layers 155 and the dielectric layers 150 are recessedto have upper surfaces with an orientation and size that conform to thespacers 332 on the bottom sides of the top source/drain regions 142. Forexample, the upper surfaces of the gate structures are parallel to(e.g., sloped at the same angle as) the bottom sides of the topsource/drain regions 142 and the spacers 332 on the bottom sides of thetop source/drain regions 142. In addition, the gate structures thatremain after recessing and removal are aligned under the widest portionsof the source/drain regions 142 including the spacers 332 thereon.

FIG. 15 is a cross-sectional view illustrating gate encapsulation layerdeposition in a method of manufacturing a semiconductor device,according to an exemplary embodiment of the present invention. Referringto FIG. 15, a gate encapsulation layer 160, comprising, for example, anitride, such as SiN, is deposited on the gate structures including thegate layers 155 and the dielectric layers 150, and on the spacers 332and 331 using ALD or other conformal deposition technique. The gaps 157(see FIG. 14) between the gate structures are pinched-off as a result ofthe deposition of the gate encapsulation layer 160.

FIG. 16 is a cross-sectional view illustrating inter-level dielectric(ILD) layer deposition in a method of manufacturing a semiconductordevice, according to an exemplary embodiment of the present invention.Referring to FIG. 16, an ILD layer 170 comprising, for example, siliconoxide (SiO_(x)), silicon oxycarbide (SiOC), silicon oxycarbonitride(SiOCN) or some other dielectric, is formed on the exposed portions ofthe structure including the deposited gate encapsulation layer 160. TheILD layer 170 is deposited using a deposition process, such as, forexample, CVD, PECVD, PVD, ALD, MBD, PLD, LSMCD, and/or spin-on coating.The deposited layer is planarized using a planarization process, suchas, for example, CMP.

FIG. 17 is a cross-sectional view illustrating patterning of the ILDlayer to form an opening for a top source/drain contact in a method ofmanufacturing a semiconductor device, according to an exemplaryembodiment of the present invention. Referring to FIG. 17, a trench 175is opened in the ILD layer 170 over the source/drain regions 142 using,for example, lithography followed by ME. According to an embodiment, theetchant is selective with respect to the layer 160. The formation of thetrench 175 exposes the encapsulation layer 160 formed on thesource/drain regions 142 and in between the gate structures.

FIG. 18 is a cross-sectional view illustrating removal of portions ofthe top spacer and gate encapsulation layers and formation of a topsource/drain contact in a method of manufacturing a semiconductordevice, according to an exemplary embodiment of the present invention.Referring to FIG. 18, exposed portions of the gate encapsulation layer160, and then of the top spacer layer 332 in the trench 175 are removed.If the gate encapsulation layer 160 is silicon nitride, it can beremoved by a wet etch containing hot phosphoric acid. The top spacer 332(e.g., silicon oxide) can be removed by a wet etch containing bufferedHF or diluted HF. Alternatively, oxide can be removed by a dry etch suchas chemical oxide etch. After removal of the portions of the gateencapsulation and top spacer layers 160 and 332, a contact tosource/drain regions 142 is formed in the trench 175 by filling thetrench 175 with a contact material layer 180, such as, for example,electrically conductive material including, but not necessarily limitedto, tungsten, cobalt, zirconium, tantalum, titanium, aluminum,ruthenium, and/or copper. A liner layer 182 including, for example,titanium and/or titanium nitride, may be formed in the trench on thesource/drain regions 142, the encapsulation layer 160 and portions ofthe top spacer layer 332 at the bottom of the trench 175, and on the ILDlayer 170 at sides of the trench 175 before filling the trench with thecontact material layer 180. The structure including a single contactregion (including layers 180 and 182) in one trench 175 to multiplesource/drain regions 142, as opposed to multiple contacts in respectivetrenches to corresponding source/drain regions, increases the area andvolume of the contact region, resulting in a lower resistance on thecontact region than when a plurality of contacts are used. As shown inFIG. 18, during removal of exposed portions of the gate encapsulationlayer 160, divots 177 are formed at the top of the portions of the gateencapsulation layer 160 between the gate structures. The divots 177,which are filled with the contact material and liner layers 180 and 182,further increase the area/volume of the contact region.

Deposition of the contact material and liner layers 180 and 182 can beperformed using one or more deposition techniques, including, but notnecessarily limited to, CVD, PECVD, PVD, ALD, MBD, PLD, LSMCD, and/orspin-on coating, followed by planarization using a planarizationprocess, such as, for example, CMP.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may bemade by one skilled in the art without departing from the scope orspirit of the invention.

We claim:
 1. A method for manufacturing a semiconductor device,comprising: forming a first semiconductor layer on a semiconductorsubstrate; forming a second semiconductor layer comprising a firstconcentration of germanium on the first semiconductor layer; forming athird semiconductor layer on the second semiconductor layer, wherein thefirst and third semiconductor layers each comprise a concentration ofgermanium which is greater than the first concentration of germanium;patterning the first, second and third semiconductor layers into atleast one fin; covering the second semiconductor layer with a masklayer; simultaneously growing a bottom source/drain region from thefirst semiconductor layer and a top source/drain region from the thirdsemiconductor layer; removing the mask layer from the secondsemiconductor layer; and forming a gate structure on and around thesecond semiconductor layer; wherein a portion of the first semiconductorlayer remains unpatterned; and wherein covering the second semiconductorlayer with the mask layer comprises: forming a first germanium oxidelayer on the first, second and third semiconductor layers of the atleast one fin and on the unpatterned portion of the first semiconductorlayer; performing a first annealing process to convert the firstgermanium oxide layer formed on the first and third semiconductor layersinto a first oxide mask layer; and removing remaining portions of thefirst germanium oxide layer from the at least one fin.
 2. The methodaccording to claim 1, wherein covering the second semiconductor layerwith the mask layer further comprises: forming a second germanium oxidelayer on the first, second and third semiconductor layers of the atleast one fin and on the unpatterned portion of the first semiconductorlayer, including on the first oxide mask layer; performing a secondannealing process to convert the second germanium oxide layer formed onthe second semiconductor layer into a second oxide mask layer; andremoving remaining portions of the second germanium oxide layer from theat least one fin and from the unpatterned portion of the firstsemiconductor layer, including from the first oxide mask layer.
 3. Themethod according to claim 2, wherein the second germanium oxide layer isthicker than the first germanium oxide layer.
 4. The method according toclaim 2, wherein the second annealing process is performed at a highertemperature than the first annealing process.
 5. The method according toclaim 2, wherein the first and second oxide mask layers comprise siliconoxide.
 6. The method according to claim 2, wherein the second oxide masklayer is thicker than the first oxide mask layer.
 7. The methodaccording to claim 6, wherein covering the second semiconductor layerwith the mask layer further comprises removing the first oxide masklayer from the first and third semiconductor layers.
 8. The methodaccording to claim 1, further comprising: forming a second germaniumoxide layer on the top and bottom source/drain regions and on the secondsemiconductor layer.
 9. The method according to claim 1, wherein thefirst, second and third semiconductor layers comprise silicon germanium.10. The method according to claim 1, further comprising performing ajunction annealing process following the simultaneous growing of thebottom and top source/drain regions.
 11. A method for manufacturing asemiconductor device, comprising: forming a first semiconductor layer ona semiconductor substrate; forming a second semiconductor layercomprising a first concentration of germanium on the first semiconductorlayer; forming a third semiconductor layer on the second semiconductorlayer, wherein the first and third semiconductor layers each comprise aconcentration of germanium which is greater than the first concentrationof germanium; patterning the first, second and third semiconductorlayers into at least one fin; covering the second semiconductor layerwith a mask layer; simultaneously growing a bottom source/drain regionfrom the first semiconductor layer and a top source/drain region fromthe third semiconductor layer; removing the mask layer from the secondsemiconductor layer; forming a gate structure on and around the secondsemiconductor layer; forming a germanium oxide layer on the top andbottom source/drain regions and on the second semiconductor layer; andperforming an annealing process to convert the germanium oxide layerformed on the top and bottom source/drain regions into top and bottomoxide spacer layers.
 12. The method according to claim 11, whereinforming the gate structure comprises: depositing a gate dielectric layerand a gate layer on the top and bottom oxide spacer layers and on thesecond semiconductor layer; and recessing the gate structure, whereinthe gate structure is self-aligned with the top source/drain region. 13.The method according to claim 12, wherein upper surfaces of the gatestructure have an orientation and size that conform to an orientationand size of the top oxide spacer layer formed on bottom sides of the topsource/drain region.
 14. A method for manufacturing a verticalfield-effect transistor, comprising: forming a first semiconductor layeron a semiconductor substrate; forming a second semiconductor layercomprising a first concentration of germanium on the first semiconductorlayer; forming a third semiconductor layer on the second semiconductorlayer, wherein the first and third semiconductor layers each comprise aconcentration of germanium which is greater than the first concentrationof germanium; patterning the first, second and third semiconductorlayers into at least one fin; covering the second semiconductor layerwith a mask layer; simultaneously growing a bottom source/drain regionfrom the first semiconductor layer and a top source/drain region fromthe third semiconductor layer; removing the mask layer from the secondsemiconductor layer; simultaneously forming top and bottom spacer layerson the top and bottom source/drain regions; and forming a gate structureon and around the second semiconductor layer; wherein simultaneouslyforming the top and bottom spacer layers comprises: forming a germaniumoxide layer on the top and bottom source/drain regions and on the secondsemiconductor layer; and performing an annealing process to convert thegermanium oxide layer formed on the top and bottom source/drain regionsinto the top and bottom spacer layers.